linux-kernel - Re: [PATCH v5 6/6] qcom/soc/drivers: Add DTPM description for sdm845

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Date:   Fri, 7 Jan 2022 11:27:54 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     rjw@...ysocki.net, lukasz.luba@....com, robh@...nel.org,
        heiko@...ech.de, arnd@...aro.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, ulf.hansson@...aro.org,
        Andy Gross <agross@...nel.org>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v5 6/6] qcom/soc/drivers: Add DTPM description for sdm845

On Sat 18 Dec 05:00 PST 2021, Daniel Lezcano wrote:

> The DTPM framework does support now the hierarchy description.
> 
> The platform specific code can call the hierarchy creation function
> with an array of struct dtpm_node pointing to their parents.
> 
> This patch provides a description of the big and Little CPUs and the
> GPU and tie them together under a virtual package name. Only sdm845 is
> described.
> 
> The description could be extended in the future with the memory
> controller with devfreq if it has the energy information.
> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>  drivers/soc/qcom/Kconfig  |  9 ++++++
>  drivers/soc/qcom/Makefile |  1 +
>  drivers/soc/qcom/dtpm.c   | 65 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 75 insertions(+)
>  create mode 100644 drivers/soc/qcom/dtpm.c
> 
> diff --git a/drivers/soc/qcom/Kconfig b/drivers/soc/qcom/Kconfig
> index e718b8735444..f21c1df2f2f9 100644
> --- a/drivers/soc/qcom/Kconfig
> +++ b/drivers/soc/qcom/Kconfig
> @@ -228,4 +228,13 @@ config QCOM_APR
>  	  application processor and QDSP6. APR is
>  	  used by audio driver to configure QDSP6
>  	  ASM, ADM and AFE modules.
> +
> +config QCOM_DTPM
> +	tristate "Qualcomm DTPM hierarchy"
> +	depends on DTPM
> +	help
> +	 Describe the hierarchy for the Dynamic Thermal Power
> +	 Management tree on this platform. That will create all the
> +	 power capping capable devices.
> +
>  endmenu
> diff --git a/drivers/soc/qcom/Makefile b/drivers/soc/qcom/Makefile
> index 70d5de69fd7b..cf38496c3f61 100644
> --- a/drivers/soc/qcom/Makefile
> +++ b/drivers/soc/qcom/Makefile
> @@ -28,3 +28,4 @@ obj-$(CONFIG_QCOM_LLCC) += llcc-qcom.o
>  obj-$(CONFIG_QCOM_RPMHPD) += rpmhpd.o
>  obj-$(CONFIG_QCOM_RPMPD) += rpmpd.o
>  obj-$(CONFIG_QCOM_KRYO_L2_ACCESSORS) +=	kryo-l2-accessors.o
> +obj-$(CONFIG_QCOM_DTPM) += dtpm.o
> diff --git a/drivers/soc/qcom/dtpm.c b/drivers/soc/qcom/dtpm.c
> new file mode 100644
> index 000000000000..c15283f59494
> --- /dev/null
> +++ b/drivers/soc/qcom/dtpm.c
> @@ -0,0 +1,65 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright 2021 Linaro Limited
> + *
> + * Author: Daniel Lezcano <daniel.lezcano@...aro.org>
> + *
> + * DTPM hierarchy description
> + */
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/dtpm.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +
> +static struct dtpm_node __initdata sdm845_hierarchy[] = {
> +	[0]{ .name = "sdm845" },

Why is the index signifiant here?
Doesn't this imply risk that we forget one element, which will be
thereby implicitly be left initialized as {} and hence denote
termination of the list?

> +	[1]{ .name = "package",
> +	     .parent = &sdm845_hierarchy[0] },
> +	[2]{ .name = "/cpus/cpu@0",
> +	     .type = DTPM_NODE_DT,
> +	     .parent = &sdm845_hierarchy[1] },
> +	[3]{ .name = "/cpus/cpu@100",
> +	     .type = DTPM_NODE_DT,
> +	     .parent = &sdm845_hierarchy[1] },
> +	[4]{ .name = "/cpus/cpu@200",
> +	     .type = DTPM_NODE_DT,
> +	     .parent = &sdm845_hierarchy[1] },
> +	[5]{ .name = "/cpus/cpu@300",
> +	     .type = DTPM_NODE_DT,
> +	     .parent = &sdm845_hierarchy[1] },
> +	[6]{ .name = "/cpus/cpu@400",
> +	     .type = DTPM_NODE_DT,
> +	     .parent = &sdm845_hierarchy[1] },
> +	[7]{ .name = "/cpus/cpu@500",
> +	     .type = DTPM_NODE_DT,
> +	     .parent = &sdm845_hierarchy[1] },
> +	[8]{ .name = "/cpus/cpu@600",
> +	     .type = DTPM_NODE_DT,
> +	     .parent = &sdm845_hierarchy[1] },
> +	[9]{ .name = "/cpus/cpu@700",
> +	     .type = DTPM_NODE_DT,
> +	     .parent = &sdm845_hierarchy[1] },
> +	[10]{ .name = "/soc@...pu@...0000",

It worries me that we encode the textual structure of the dts in the
kernel. E.g. for quite a while this was "/soc/gpu@...0000", so if this
landed a year ago this driver would have prevented us from correcting
the dts.

Another concern is that not all busses in the system are capable of
36-bit wide addresses, so it's plausible that we might one day have to
create a more accurate representation of the address space. Maybe not on
SDM845, but this would force us to be inconsistent.

Regards,
Bjorn

> +	     .type = DTPM_NODE_DT,
> +	     .parent = &sdm845_hierarchy[1] },
> +	[11]{ },
> +};
> +
> +static struct of_device_id __initdata sdm845_dtpm_match_table[] = {
> +        { .compatible = "qcom,sdm845", .data = sdm845_hierarchy },
> +        {},
> +};
> +
> +static int __init sdm845_dtpm_init(void)
> +{
> +	return dtpm_create_hierarchy(sdm845_dtpm_match_table);
> +}
> +late_initcall(sdm845_dtpm_init);
> +
> +MODULE_DESCRIPTION("Qualcomm DTPM driver");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:dtpm");
> +MODULE_AUTHOR("Daniel Lezcano <daniel.lezcano@...nel.org");
> +
> -- 
> 2.25.1
>